1. Field of the Invention
The present invention generally relates to a shift mechanism for a marine propulsion unit, and more particularly relates to an improved gear clutching construction for a marine propulsion unit.
2. Description of Related Art
Marine propulsion units, such as outboard motors, incorporate an engine as a prime mover to power a marine propulsion device. The propulsion device typically is a propeller and is submerged when an associated watercraft rests on a body of water. The engine typically is placed atop the outboard motor. A drive train and a transmission couple the engine with the propulsion device. Typically, the engine has a crankshaft extending generally vertically. The drive train includes a driveshaft disposed within a housing unit below the engine. The driveshaft also extends generally vertically and is connected to the crankshaft to transfer the power of the engine to a propulsion shaft which also is included in the drive train. The propulsion shaft extends generally normal to the driveshaft. The transmission couples the propulsion shaft with the driveshaft.
The outboard motor can incorporate a shift mechanism that shifts the transmission among forward, neutral and reverse modes. The forward and reverse modes are driving modes and the neutral mode is a non-driving mode. The propeller rotates in a direction such that the associated watercraft proceeds forward when the transmission is in the forward mode, while the propeller rotates in another direction such that the watercraft proceeds backward when the transmission is in the reverse mode. Otherwise, the propeller does not rotate due to engine output when the transmission is in the neutral mode because the propulsion shaft is decoupled from the driveshaft in this mode.
FIGS. 1-3 illustrate a typical arrangement of the shift mechanism and transmission. FIG. 1 is a partial side elevation view of a conventional outboard motor. FIG. 2 is an elevation view of a sleeve of the shift mechanism. FIG. 3 is a cross-sectional view of the sleeve taken along the line 3—3 of FIG. 2, the sleeve being coupled with a forward or reverse gear.
The shift mechanism, which is indicated by the reference numeral 20, shifts a transmission that includes a pinion 24 and forward and reverse gears 28, 30 among forward, reverse and neutral modes. The driveshaft 22 carries the pinion 24 at the shaft's bottom end. The propulsion shaft 26 carries the forward and reverse gears 28, 30 that always mesh with the pinion 24. The shift mechanism 20 includes a sleeve 32 that is slidably disposed between the forward and reverse gears 28, 30 on the propulsion shaft 26 and is coupled with the propulsion shaft 26 so as to rotate together with the propulsion shaft 26. The forward and reverse gears 28, 30 have teeth 34 and the sleeve 32 has recesses 36. The teeth 34 can engage with the recesses 36. The sleeve 32 is driven by the forward or reverse gear 28, 30 while the teeth 34 engage with walls of the recesses 36. That is, the driving force of the forward or reverse gear 28, 30 is transferred to the sleeve 32 from the gear 28, 30 while surfaces 38 of the teeth 34 abut on the surfaces 40 of the recesses 36. The propulsion shaft 26 and sleeve 32 thus can rotate with the driveshaft.
A mechanical shift actuator selectively connects the sleeve 32 either with the forward gear 28 or the reverse gear 30, or disconnects the sleeve 32 from both the forward and reverse gears 28, 30. Because the sleeve 32 is rotationally coupled with the propulsion shaft 26, the propulsion shaft 26 rotates in the forward propelling direction when connected with the forward gear 28, while the propulsion shaft 26 rotates in the reverse propelling direction when connected with the reverse gear 30. Otherwise, the propulsion shaft 26 is not driven for rotation by the engine when the sleeve 32 is not connected with either of the gears 28, 30. The shift mechanisms are disclosed, for example, in U.S. Pat. Nos. 4,579,204, 5,006,084, 5,445,546, 5,556,312, 5,556,313, 5,788,546, 5,839,928 and 6,123,591 and Japanese Patent Publications Nos. 59-73627 and 07-67918.